Non-recirculating and recirculating inertial flows of an elasto-viscoplastic yield stress fluid (Carbopol (R) gel) around a cylinder were studied experimentally. The experimental set-up that was designed and built was validated by studying the flow of a Newtonian fluid. Appropriate procedures were introduced for yield stress fluids. Changes in the morphology of the flow behind the cylinder were studied for Oldroyd numbers between 0 and 0.5 and Reynolds numbers between 10 and 100. The characteristic lengths of the flow and the separation angle of the streamlines were determined. They were compared with the numerical predictions for a Herschel-Bulkley viscoplastic fluid. The limits between the different flow regimes were determined experimentally and compared with the numerical results. The influence of the boundary conditions, and in particular slip on the cylinder, were also evaluated experimentally. (c) 2012 Elsevier B.V. All rights reserved.